Continuously-variable-ratio transmissions of the toroidal-race rolling-traction type

ABSTRACT

A continuously-variable ratio transmission of the toroidal-race rolling-traction type, especially in and for an automobile vehicle. The ratio transmitted by the rollers (10) is determined by the position of a double-ended piston (15), the ends of which move in cylinders (17, 16) respectively connected to further cylinders (31, 36) the pistons (33, 38) of which are movable by the opposite limbs of a rocking pedal (42) controlled by the operator. Rocking of the pedal in one direction depresses one such piston (e.g. 33) and releases the other, thereby moving the double-ended piston (15) in one direction and so inducing ratio change in one sense, while rocking the pedal in the opposite direction has the opposite effect. The cylinders (31, 36) of the pedal-controlled pistons may be mounted in a fluid reservoir (34), and formed with ports through which the fluid lines are topped-up from the reservoir each time the pistons (33, 38) rise close to the tops of their strokes.

This invention relates to continuously-variable-ratio transmissions(CVT's) of the known toroidal-race, rolling-traction type, in which thetransmitted ratio is determined by the variable orientation of rollersthat roll in contact with a part-toroidal race formed on a rotatinginput disc, and with a similar race formed on a coaxial andcontra-rotating output disc. The invention relates particularly to CVT'sof this type in which the variable orientation of the rollers isdetermined hydraulically by the piston position of a hydraulic ram. Someessential components of such a CVT are illustrated schematically in FIG.1A and 1B of the accompanying drawings, in which an input disc 1, formedwith a part-toroidal race 2, is splined at 3 to an input shaft 4rotatable about an axis 5. The splined connection at 3 causes disc 1 andshaft 4 to rotate together, but allows limited relative axial movementbetween them. An output disc 6 is mounted on an output shaft 7 which isalso rotatable about axis 5. A part-toroidal race 8 is formed on disc 6so that the surfaces of races 2 and 8 belong to the surface of a commontorus formed about the same axis 5 as the shafts 4 and 7. A roller 10,which will typically be one of a set of three such rollers located at120° angular spacing around axis 5, rolls in contact with races 2 and 8,and an appropriate "end load", as indicated at 9, is exerted upon thediscs to urge them axially-together and so achieve the necessarytraction-transmitting reaction between the discs and the rollers. Bothmechanical and hydraulic means of generating such an end load are wellknown in the art. By tilting the rollers 10 about a diameter asindicated by arrow 11, the transmitted ratio will be varied. Withrollers 10 as shown, contacting input disc 1 at a large radius andoutput disc 6 at a smaller radius, output disc 6 will rotate faster thaninput disc 1 and the CVT will therefore be in "high" ratio. If rollers10 are tilted to an opposite position in which they contact input disc 1at a small radius and output disc 6 at a larger radius, the CVT will bein "low" ratio. As the arrowed detailed view shows, each roller 10rotates about an axis 12 within a bearing 13 mounted on a rollercarriage 14. In a manner which is known in the art, and shown by way ofexample in patent specification U.S. Pat. No. 4,662,248, the oppositeends of each carriage 14 of the set of three are formed as pistons 15mounted to move within cylinders 16 and 17, and the two cylinders areconnected by way of hydraulic lines 18, 19 with different outlets of acontrolled valve system 20 which is itself in communication both with asource 21 of fluid under pressure and with a drain 22. Each carriage 14and its cylinders 16, 17 are mounted so that the common axis 23 of thepistons and cylinders, which also constitutes a diameter of the roller10, lies substantially tangential to the centre circle of the commontorus of which the races 2 and 8 form part of the surface. The pistons15 and with them the carriage 14 and roller 10 can not only move backand forth along axis 23. They can also rotate about the axis, and whenthey do so the radii (relative to axis 5) at which the rollers contactraces 2 and 8 change also, thereby changing the transmitted ratio. As iswell know in the art, such a CVT is in equilibrium when the sum of thereactions of each roller 10 against its races, resolved in a directionparallel to the axis 23, is balanced by the nett axial force exertedupon that roller by the fluid in the chambers of cylinders 16 and 17. Ifthe equilibrium is disturbed, initiated either by a change of reactionat the disc/roller interfaces or by an operator demand on valve system20 and a consequent change in the nett hydraulic force exerted upon thecarriage by cylinders 16 and 17, the carriage will move axially, andthis movement will be accompanied by a rotation and a change intransmitted ratio until equilibrium is restored at the appropriate newratio.

A hydraulically-operated CVT, having features of the kind just describedin outline, is described in more detail in patent specificationGB-C-2023753 as well as in U.S. Pat. No. 4,662,248. Thehydraulically-controlled CVT described in GB-C-2023753 is intended toachieve optimum performance in the high-powered driveline of a car orcommercial vehicle. In such an application, very sophisticatedregulation by mechanisms such as item 20 above is necessary to respondto road conditions, driver demand etc. in a manner which continuouslymaintains the right balance of pressures in cylinders 16 and 17. A vitalcomponent in such a CVT is of course a high powered pump (item 21 above,items 174, F, in the drawings of GB-C-2023753, U.S. Pat. No. 4,662,248respectively). It is an aim of the present invention to adapt andsimplify such a hydraulically-controlled CVT for use where no such powerdriven pump is available and where less exact pressure balances willsuffice. Instead, the necessary hydraulic forces are generated, withinan essentially closed-loop hydraulic system, by physical work done by ahuman operator, for instance the driver of the vehicle in which the CVTwill typically be fitted. The CVT according to the invention istherefore to be distinguished from the kind of CVT shown for instance inPatent Specification GB-A-1494128, in which an operator-controlled leveris directly connected to a piston/cylinder unit forming part of ahydraulic circuit within the CVT. However the ratio transmitted by theCVT is determined by a quite separate connection--in that example, adirect mechanical connection--between the lever and those parts of theCVT whose relative movement causes the ratio to change. In GB-A-1494128,the hydraulic circuit serves essentially as part of a feedback system,to give to the operator, by way of the lever, a reaction which providessome "feel" for the ratio-changes that he has brought about by way ofthe direct mechanical connection.

SUMMARY OF THE INVENTION

According to the present invention we provide a continuously-variableratio transmission (CVT) including a double-acting hydraulic ramcomprising a piston and a pair of opposed hydraulic cylinders, and inwhich the fluid contents of both cylinders are connected to physicaldisplacement means operable by a human operator, and characterised inthat the CVT is of the toroidal-race rolling-traction type, in that theratio transmitted by the traction-transmitting rollers is determined bythe position of the piston, and in that the physical displacement meanscomprise separate physical displacement members connected to the opposedhydraulic cylinders of the ram whereby by simultaneously depressing onemember, and releasing the other, the operator changes the transmittedratio by displacing the ram piston by which that ratio is determined.

The two displacement members may be connected to opposite arms of arocking pedal or other lever.

The members may be pistons movable within respective hydrauliccylinders, each cylinder being mounted within a hydraulic reservoir andhaving a filler port for hydraulic fluid formed in the cylinder wall,whereby release of the piston beyond a certain point exposes the workingspace of the cylinder cavity to the reservoir and so tops up thehydraulic line between that member and the ram, in readiness for thenext depression of the member. The members may move in parallelcylinders whose axes lie in the plane of rotation of the rocking pedal,and the action of the lever may be such as to promote a mode ofoperation in which the fluid volume swept by the piston depressed, byany actuation of the pedal, tends slightly to exceed the volume swept bythe pedal released, and so tends automatically to maintain the hydraulicsystem filled with fluid and to avoid cavities. This may be achieved bygiving the rocking pedal the form of an angled lever, in which the pivotaxis is displaced from the straight line joining the two points throughwhich the lever makes contact with the two pistons or other displacementmembers.

The invention particularly includes an automobile vehicle including sucha CVT.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B diagrammatically illustrate the essential components ofa CVT;

FIG. 2A diagrammatically shows the components for the CVT of anautomobile vehicle; and

FIG. 2B diagrammatically shows an automobile vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be described, by way of example, with referenceto FIGS. 2A and 2B of the accompanying drawings, which shows componentsof the CVT for an automobile vehicle diagrammatically and/orschematically.

FIG. 2 does not show the input disc 1 and output disc 6 of FIG. 1, butit does show all three of the set of rollers 10 that transmit tractionbetween them. As before, each roller 10 pivots about an axis 12 in abearing 13 mounted on its carriage 14, and the carriage ends are formedas pistons 15 moving within cylinders 16 and 17. FIG. 2 also makes itclear that all the cylinders 16 in the set are hydraulically connectedby lines 18, and that all cylinders 17 are similarly connected by lines19, so ensuring that the cylinder pressures acting on all the carriagesare equal at all times, and so promoting the transmission of exactly thesame ratio by all the rollers 10 at all times. This method of equalisingthe ratio angles of all the rollers is also known generally in the art,and taught specifically in U.S. Pat. No. 4,662,248. According to theinvention however, and as shown in FIG. 2, line 19 also connectscylinders 17 to the outlet 30 of a cylinder 31 containing a compressionspring 32 and a piston 33. Similarly, line 18 connects all the cylinders16 to the outlet 35 of a cylinder 36 containing a compression spring 37and a piston 38. Cylinders 31, 36 are mounted within a hydraulic fluidreservoir 34 and inlet ports 39, 40 are located at high level within theside walls of cylinders 31, 36 respectively, so that they come intocommunication with the working spaces of their cylinders only when therespective pistons 33, 38 are close to the tops of their strokes. A rod41 connects a rounded recess formed in the top of piston 33 with acorresponding recess formed in the underside of a pedal 42, mounted torock about a pivot 43, and a similar and parallel rod 44 connects asimilar recess on the top surface of piston 38 with another recessformed on the underside of pedal 42 but this time to the other side ofpivot 43.

Pedal 42 is intended to be operated by the foot of the operator of theCVT, for instance the driver of a vehicle in which the CVT is used. Ifthe driver pivots pedal 42 clockwise about pivot 43, so that rod 44 andpiston 38 are depressed while rod 41 and piston 33 are released, thepressures in all of cylinders 16 will rise equally, while the pressuresin all of cylinders 17 will fall equally. Carriages 14 will alltherefore tend to move to the left, so that the angular setting of allthree of rollers 10 about their respective axes 23 will change equally,so altering the transmitted ratio. Conversely, if pedal 42 is pivotedanti-clockwise about pivot 43, the pressure will rise in cylinders 17and fall in cylinders 16, so that the angular setting of rollers 10 willchange in the opposite sense and so alter the transmitted ratio in theopposite sense also. If the driver pivots pedal 42 fully clockwise, sothat piston 38 is fully depressed and rollers 10 are at thecorresponding extreme of their angular range, piston 33 rises highenough to uncover port 39, so allowing fluid from reservoir 34 to entercylinder 31 and make up for any fluid losses that may have occurred inline 19 or the rest of the left-hand side of the system. Similarly, ifpedal 42 is pivoted fully anti-clockwise, port 40 will uncover and theright-side of the system will be topped up.

Only a single input disc (1) and output disc (6) are shown in FIG. 1,and CVT's of the toroidal-race rolling-traction type, having only asingle such disc of each kind, are known in the art and are oftendescribed as "single-side" or "single-ended". However the type of CVTshown in GB-C-2023753 and U.S. Pat. No. 4,662,248 is perhapsbetter-known in the art, and is often called "double-sided". Typically,in such a CVT, a single output disc, formed with a toroidal race on eachof its faces, is located between two coaxial and inwardly-facing inputdiscs which rotate together. One set of rollers (such as items 10)transmits traction between one of the input discs and one of the raceson the output disc, and a second set of rollers transmits tractionbetween the other input disc and the other output disc race. It is ofcourse vital that at any one time all the rollers, whether in one set orthe other, lie at the same angular setting and so transmit the sameratio between their respective input and output races. This is easilyachievable in principle by the control system shown in FIG. 2; thehydraulic lines 18, 19 may connect not only (as shown) the cylinders 16and 17 of one set of rollers, but also, as indicated at 45 and 46, maygo on to supply the corresponding cylinders of a second or evensubsequent sets of rollers.

By locating pivot 43 on a flange 47, as shown, a useful effect may beobtained. Pivot point 43 is thus displaced from the imaginary straightline 48 which joins the recesses at which rods 41, 44 make contact withlever 42. Reference 49 indicates another imaginary line, which passesthrough pivot 43 and lies at right angles to rods 41 and 44. Providedthe system is designed so that the heads of the two rods never passbelow line 49, then whenever lever 42 is pivoted clockwise, so thatpiston 38 is depressed and piston 33 released, the fluid volume swept bydepressed piston 38 will exceed that swept by released piston 33.Similarly, if lever 42 is pivoted anti-clockwise, the volume swept bydepressed piston 33 will exceed that swept by released piston 38.Provided the offset of pivot 43 from line 48 is small the excess will besmall also, and without distorting the normal operation of the systemwill have the effect of promoting a small positive pressure at all timeswithin the closed hydraulic circuit, so helping to avoid the formationof vacuums and other cavities.

As already indicated the invention applies not only to CVT's but also toautomobile vehicles including them. In the arrowed insert to FIG. 2A,labelled as FIG. 2B, such a vehicle is indicated in outline at 51 andits engine schematically at 52. The CVT, including for example partsillustrated in the rest of FIG. 2, is indicated at 53 schematically, asare the connection 54 between the CVT output and the driven wheels 55 ofthe vehicle.

I claim:
 1. A continuously-variable-ratio transmission (CVT) including adouble-acting hydraulic ram comprising a piston (15) and a pair ofopposed hydraulic cylinders (16, 17), and in which the fluid contents ofboth cylinders are connected to physical displacement means (31, 36, 42)operable by a human operator, wherein the CVT is of the toroidal-racerolling-traction type, the ratio transmitted by traction-transmittingrollers (10) of the CVT is determined by the position of the piston(15), and the physical displacement means comprise two separate physicaldisplacement members (33, 38) connected hydraulically and respectivelyto the opposed hydraulic cylinders (17, 16) of the ram whereby bysimultaneously depressing one said displacement member (33) andreleasing another said displacement member (38) the operator changes thetransmitted ratio by displacing the ram piston (15) by which that ratiois determined, and the two displacement members (33, 38) thus depressedand released are connected to opposite arms of a rocking member (42). 2.A CVT according to claim 1, wherein the two displacement members (33,38) are pistons movable within respective hydraulic cylinders (31, 36),each cylinder having a cylinder wall and being mounted within ahydraulic reservoir (34) and having a filler port (39, 40) for hydraulicfluid formed in the cylinder wall, whereby release of the piston beyonda certain point exposes a working space of the cylinder cavity to thereservoir and so tops up the hydraulic line (19, 18) between that memberand the ram, in readiness for a next depression of the member.
 3. A CVTaccording to claim 1, wherein the two displacement members and therocking member are so arranged that the fluid volume swept by thedisplacement member depressed by operation of the member exceeds thefluid volume simultaneously swept by the displacement member released.4. A CVT according to claim 3, wherein the rocking member (42) has arocking pivot (43) which is displaced from a straight line (48) joiningthe points through which the member makes contact with each of the twodisplacement members.
 5. An automobile vehicle comprising acontinuously-variable-ratio transmission (CVT) including a double-actinghydraulic ram comprising a piston (15) and a pair of opposed hydrauliccylinders (16, 17), and in which the fluid contents of both cylindersare connected to physical displacement means (31, 36, 42) operable by ahuman operator, wherein the CVT is of the toroidal-race rolling-tractiontype, the ratio transmitted by traction-transmitting rollers (10) of theCVT is determined by the position of the piston (15), and the physicaldisplacement means comprise two separate physical displacement members(33, 38) connected hydraulically and respectively to the opposedhydraulic cylinders (17, 16) of the ram whereby by simultaneouslydepressing one said displacement member (33) and releasing another saiddisplacement member (38) the operator changes the transmitted ratio bydisplacing the ram piston (15) by which that ratio is determined, andthe two displacement members (33, 38) thus depressed and released areconnected to opposite arms of a rocking member (42).